Ruling Out Pulmonary Embolism in Primary Care: Comparison of the Diagnostic Performance of "Gestalt" and the Wells Rule.

Purpose: Diagnostic prediction models such as the Wells rule can be used for safely ruling out pulmonary embolism (PE) when it is suspected. A physician's own probability estimate ("gestalt"), however, is commonly used instead. We evaluated the diagnostic performance of both approaches in primary care.

Methods: Family physicians estimated the probability of PE on a scale of 0% to 100% (gestalt) and calculated the Wells rule score in 598 patients with suspected PE who were thereafter referred to secondary care for definitive testing. We compared the discriminative ability (c statistic) of both approaches. Next, we stratified patients into PE risk categories. For gestalt, a probability of less than 20% plus a negative point-of-care d-dimer test indicated low risk; for the Wells rule, we used a score of 4 or lower plus a negative d-dimer test. We compared sensitivity, specificity, efficiency (percentage of low-risk patients in total cohort), and failure rate (percentage of patients having PE within the low-risk category).

Results: With 3 months of follow-up, 73 patients (12%) were confirmed to have venous thromboembolism (a surrogate for PE at baseline). The c statistic was 0.77 (95% CI, 0.70-0.83) for gestalt and 0.80 (95% CI, 0.75-0.86) for the Wells rule. Gestalt missed 2 out of 152 low-risk patients (failure rate = 1.3%; 95% CI, 0.2%-4.7%) with an efficiency of 25% (95% CI, 22%-29%); the Wells rule missed 4 out of 272 low-risk patients (failure rate = 1.5%; 95% CI, 0.4%-3.7%) with an efficiency of 45% (95% CI, 41%-50%).

Conclusions: Combined with d-dimer testing, both gestalt using a cutoff of less than 20% and the Wells rule using a score of 4 or lower are safe for ruling out PE in primary care. The Wells rule is more efficient, however, and PE can be ruled out in a larger proportion of suspected cases.